It has been blamed by Oprah Winfrey as "the root of all the problems in the world". It causes not just gun crime and drug use, but relationship problems ranging from domestic violence to an inability to commit. Can you guess what it is? No, it's not poverty, stupid. It's low self-esteem (sorry I called you stupid). Self-help books tell us we must love ourselves before we can have a healthy relationship, but there's no evidence that low self-esteem causes such problems; indeed, too much self-esteem may be more likely to make you a loser in love.

Self-esteem was defined by US psychologist William James in 1890 as being "determined by the ratio of our actualities to our supposed potentials". If only they'd left it there. Somehow it became central to life: where it was low, it caused dismal relationships; where it was high, people basked in happy marriages and glorious sex lives.

There is a standard measure for self-esteem, devised by sociologist Morris Rosenberg, that asks, say, how much you agree with statements such as "I feel I do not have much to be proud of". A low score will not necessarily ruin your life, however: a London School of Economics report found that low self-esteem causes hardly any of the things for which it is blamed. Instead, some behaviours - domestic violence and alcohol misuse, say - are more associated with high self-esteem.

This chimes with Jean Twenge and W Keith Campbell's new book, The Narcissism Epidemic. "There isn't an epidemic of low self-esteem," Twenge says. "Students have been increasingly likely to agree with statements like, 'I think I am a special person.' If anything, the studies suggest many people have too much self-esteem."

And the cause of this overdose of self-importance? "Parents ... are so anxious not to damage their little darling's self-esteem that they are loth to criticise and over-anxious to praise. If you raise self-esteem too high, you can raise a child to be narcissistic." And narcissistic children grow up to be narcissistic adults, and that's not good for relationships. "They like looking good with someone, but they fail to have any depth in their relationships and they're not into commitment."

Her co-author's research found that narcissists believe they are unique and smarter than others. They tend to be manipulative, selfish and unfaithful; not interested in intimacy because they already have someone to love: themselves. The message for parents is to limit children's choices and not treat them like royalty. "It's not good for your daughter's future relationships to get her a T-shirt saying 'Daddy's expensive little princess'," says Twenge.

If you are unconvinced of the perils of high self-esteem, be advised that self-help books may not work - one recent study found that mantras such as "I deserve the best", which are meant to make us feel better about ourselves, actually make us feel worse.